Re: [PATCH 12/30] x86, kaiser: map GDT into user page tables

[Dave Hansen]

On 11/20/2017 12:46 PM, Andy Lutomirski wrote:
>>> +     /*
>>> +      * We could theoretically do this in setup_fixmap_gdt().
>>> +      * But, we would need to rewrite the above page table
>>> +      * allocation code to use the bootmem allocator.  The
>>> +      * buddy allocator is not available at the time that we
>>> +      * call setup_fixmap_gdt() for CPU 0.
>>> +      */
>>> +     kaiser_add_user_map_early(get_cpu_gdt_ro(0), PAGE_SIZE,
>>> +                               __PAGE_KERNEL_RO | _PAGE_GLOBAL);
>> This one is needs to stay.
> When you rebase on to my latest version, this should change to mapping
> the entire cpu_entry_area.

I did this, but unfortunately it ends up having to individually map all
four pieces of cpu_entry_area.  They all need different permissions and
while theoretically we could do TSS+exception-stacks in the same call,
they're not next to each other:

 GDT: R/O
 TSS: R/W at least because of trampoline stack
 entry code: EXEC+R/O
 exception stacks: R/W